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75 Commando Spark and No Spark
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TOPIC: 75 Commando Spark and No Spark

75 Commando Spark and No Spark 23 Jun 2023 18:03 #1

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Currently working on a 75 Commando and noticed that the bike has spark when I use the starter and no spark when I kick it over. It has a brand new battery that is holding a charge of 12.8 volts.

Right now I am thinking it could be a bad kill switch. But, being this bike is a original and never really been apart I would hate to cut up the nicely tucked wiring harness.
When I hot wire from the negative battery to the negative coil. I have spark when kicking over.

what are your thoughts?

thank you

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Christopher West GySgt USMC Ret.

75 Commando Spark and No Spark 23 Jun 2023 19:13 #2

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1. Ballast resistor any good....1.5 ohms Disconnected both ends
2. run switch off-on-off switch in center position? or other style ON-OFF only
3. Power on white/yellow- will supply 12.8 to ballast resistor to feed coils
4 white purple is closest to coil end of ballast, gives power while starter cranking only
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Dave Comeau
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75 Commando Spark and No Spark 24 Jun 2023 13:01 #3

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1. Ballast resistor any good....1.5 ohms Disconnected both ends
Ballast is 2.5 ohms

2. run switch off-on-off switch in center position? or other style ON-OFF only
off-on-off switch

3. Power on white/yellow- will supply 12.8 to ballast resistor to feed coils.
Interesting that I only get .3 volts out of the white/yellow wire. and .4 out of the white/purple wire.

4 white purple is closest to coil end of ballast, gives power while starter cranking only
its just the white/ purple wire and the white/yellow attached to the ballast.

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Christopher West GySgt USMC Ret.

75 Commando Spark and No Spark 24 Jun 2023 13:01 #4

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1. Ballast resistor any good....1.5 ohms Disconnected both ends
Ballast is 2.5 ohms

2. run switch off-on-off switch in center position? or other style ON-OFF only
off-on-off switch

3. Power on white/yellow- will supply 12.8 to ballast resistor to feed coils.
Interesting that I only get .3 volts out of the white/yellow wire. and .4 out of the white/purple wire.

4 white purple is closest to coil end of ballast, gives power while starter cranking only
its just the white/ purple wire and the white/yellow attached to the ballast.

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Christopher West GySgt USMC Ret.

75 Commando Spark and No Spark 24 Jun 2023 16:10 #5

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I think I found the issue and I would assume its the Kill switch. Because I jumped the white wire and the white/yellow wire together in the headlight bucket and I got spark and 12.8 volts to the ballast resistor.

From what I hear is that a 75 switch cluster is really hard to find. I am wondering if anyone has a contact info of someone that can rebuild it.

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Christopher West GySgt USMC Ret.

75 Commando Spark and No Spark 24 Jun 2023 18:05 #6

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last time I bought stuff from norvil, I bought 2 rare new sparx repops.
NOS is not comon almost unobtanium.
WHY?
They are super tender at the throttle cable boss, and the pot metal breaks so the cable no longer will attach. also they are the only metric thread on the bike.
Triumphs in that period used the same lucas switchgear minus the start button.
Never heard of parts.....

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Dave Comeau
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